1. Field of Disclosure
The present disclosure relates to improvements in bar code symbol reading systems employing laser scanning beams having improved laser beam characteristics which enable the reading of poor quality and/or damaged bar code symbols with enhanced levels of performance.
2. Brief Description of the State of Knowledge in the Art
It is well known that poor quality bar codes and damaged bar codes typically results in decreased throughput at the retail point of sale (POS).
Various techniques have been developed to read poor quality bar codes and damaged bar codes. Such techniques include using: (i) adaptive signal processing gain adjustments and threshold levels (usually performed over a period of several sweeps across the bar code); (ii) reduced signal processing bandwidth to limit high frequency components of scanned data (i.e. limits scanner resolution); (iii) improved decode algorithms to allow for noise in bar code printing; and (iv) stitching algorithms to acquire a full decode out of partially successful attempts to acquire a whole bar code result.
In addition to the above techniques, it is well known to use of an elongated laser beam in the cross-sectional direction of laser beam scanning motion, so as to help average out spatial noise and improve the signal to noise (SNR) of the laser scanning bar code reading system. This technique can be used to read both 1D and 2D stacked bar code symbols.
For example, U.S. Pat. No. 5,621,203 discloses the use of an elongated laser beam for scanning 2D stacked bar code symbols and detecting reflected light using a linear image detector. As disclosed, the elongated laser beam which diverges in the elongated cross-sectional dimension. Also, the elongated cross-sectional dimension of the beam, in the plane of the symbol, is preferably long enough to illuminate the entirety of one dimension of a row of the symbol, at one time. The beam preferably does not converge to a waist in the elongated cross-sectional dimension.
FIG. 1 shows a bar code symbol reader 1 scanning a conventionally-elongated laser beam 10 across a bar code symbol 116. FIG. 2A1 shows a good quality UPC bar code symbol being scanned by the conventionally elongated laser scanning beam 10 from the bar code symbol reader of FIG. 1. The reflectance intensity profile produced while scanning this good quality code symbol with the conventionally elongated laser scanning beam 10 is shown in FIG. 2A2.
FIG. 2B1 shows a degraded UPC bar code symbol being scanned by a conventionally elongated laser scanning beam 10 generated from the laser scanning bar code symbol reader of FIG. 1. FIG. 2B2 shows the reflectance profile produced from the degraded bar code symbol using the conventionally elongated laser scanning beam produced from bar code symbol reader of FIG. 1.
FIG. 2C1 shows the second layer of a good quality stacked 2D bar code symbol being scanned by a conventionally elongated laser scanning beam 10 produced from the laser scanning bar code symbol reader of FIG. 1. FIG. 2C2 shows the reflectance profile produced from stacked 2D bar code symbol using the conventionally-elongated laser scanning beam 10 produced from the bar code symbol reader of FIG. 1.
Using conventionally-elongated laser beams to scan bar code symbol structures with 2D surface noise smoothes out (i.e. via spatial averaging) the reflection intensity profile of such code symbols which, in turn, increases the signal to noise (SNR) performance of the bar code symbol reader.
The elongation ratio (ER) of a laser beam, defined as the ratio of laser beam height (y) over laser beam width (x) measured along the direction of beam travel (Z) of the laser scanning beam, provides a measure of how much the laser beam is elongated along the cross (i.e. y) scan dimension of the beam, relative to the scan dimension (i.e. x direction). For known conventional laser scanning systems, the laser beam elongation ratio (ER) measures in the range of 1 to about 4.5, across the working range of conventional laser scanning bar code symbol reading systems, as illustrated in FIG. 2D.
However, hitherto, little has been known or disclosed about how to optimize the beam elongation ratio (ER) for a laser scanning bar code symbol reading system, so as to achieve enhanced levels of SNR performance when reading poor quality or damaged bar code symbols of various kinds of symbologies (e.g. UPC, GS1 2D stacked bar codes, etc).
Thus, there is a great need for improvement in the SNR of reflection intensity signals detected during laser scanning bar code symbols, and for this improvement to be achieving using laser scanning beams having optimized laser beam characteristics, while avoiding the shortcomings and drawbacks of prior art apparatus and methodologies.